Is the v5 vampire virus real?

No. No more than the Easter Bunny or the Tooth Fairy.

It appears that the V5 myth rose out of the British TV
miniseries Ultraviolet in which the the word "vampire" is
never uttered. The government backed vampire hunting squad the main
character discovers subtitutes "Code 5" or the Roman numeral V to
denote cases and targets. Hence, V5.

A number of vampire enthusiasts who have taken role playing and
fantasy a bit too far, latched on to the misattribution, and
adopted it as the rationalization of bizarre, unstable
behavior.

More recently, the V5 myth has transformed slightly, and become
the K-17 Virus myth. Rather than transliterate from the film,
vampire fans stole the idea directly from the 2002 movie Reign
in Darkness. Vampire apocalypse movies such as these seem to
bring dysfunction out of the woodwork.